Generally, in the case of weak light, people's eye may look red when using flash lamp to take photos. This is called “red eye effect”. Red eye effect occurs due to the reflection of blood vessels on the retina when the incoming light emitted by the flash lamp is very strong. However, since the digital camera is getting smaller and smaller, the distance between the flash lamp and the lens becomes shorter and shorter. Such problem is increasingly significant.
Nowadays, many cameras have been equipped with auto anti-red eye function. Such function can be categorized into two types of techniques. One is to prevent red eye using a pre-flash. The other is to perform image processing to remove red eye.
CN patent application No. CN 1100814A (published on Mar. 29, 1995) discloses an apparatus which uses pre-flash to make the pupil contracted and reduces the reflected red light. However, such apparatus can only mitigate the red eye effect to some extent, and it cannot remove the red eye thoroughly. Moreover, since pre-flash can make people look unnatural, and two flashes may consume more energy, the actual application may not achieve a desirable effect.
CN patent application No. CN 1750017A (published on Mar. 22, 2006) discloses a method for removing red eye by post-processing. The method performs facial recognition on the image where red eye occurs or uses other target detection method for locating the red eye area. Then, the information such as the color in the red eye area is adjusted so as to remove the red eye. However, in such method, the detection speed is slow and is subject to noise and is not precise and can rarely achieve the practical application in handheld or mobile devices.
JP patent application No. 2000-299812A (published on Oct. 24, 2000) discloses a photo taking device. By taking a photo with the flash light and taking a photo without the flash light and extracting the data in the red eye area based on the relation between the two photos, the red eye is removed. However, such method requires taking two photos at the same place at the same time, which extends the photo taking time and decreases the efficiency due to repetitive shooting.